The present invention relates to a device for coupling a liquid chromatograph and a mass spectrometer.
Chromatographs are effective apparatus for separating and analyzing mixture samples containing different components. When a mass spectrometer is connected as a detecting means to the chromatograph, a large amount of information about molecular weights and molecular structures can be obtained. It is relatively easy to connect a mass spectrometer to a gas chromatograph, and this combination has been extensively used to date. However, an instrument combining a mass spectrometer with a liquid chromatograph requires various considerations, because liquid must be introduced into the high-vacuum mass spectrometer. It is difficult to attain a satisfactory performance. Accordingly, the combination of a liquid chromatograph and a mass spectrometer is less widely used than the combined gas chromatograph/mass spectrometer.
A prior art instrument combining a mass spectrometer with a liquid chromatograph is shown in FIG. 1. The chromatograph 1 is indicated schematically. The mass spectrometer has an ionization chamber 2 which is formed in an ion source block 4. The outer wall of the ion source is indicated by numeral 3. Mounted between the ionization chamber 2 and the chromatograph 1 is an interface body 5 having a chamber 6 which is evacuated to a low pressure by a vacuum pump 7. In this body 5, a feed nozzle 8 is disposed opposite to a receiver nozzle 9. The feed nozzle 8 is connected to the chromatograph 1, while the receiver nozzle 9 is connected to the ionization chamber 2. The feed nozzle 8 consists of a dual tube 10 and an apertured plate 11 disposed at the front end of the tube 10. The effluent from the chromatograph 1 is conveyed through the inner tube of the double tube 10 to the position of the plate 11 at the front end. Then, the effluent is partially ejected toward the receiver nozzle 9 through the apertured plate 11. The remaining effluent is moved out of the low-pressure chamber through the outer tube of the double tube 10, and then discharged via a discharge tube 12 and a flow control valve 13. The receiver nozzle 9 is connected to the ionization chamber 2 by means of a passage 14, which is heated by a heater 15.
The device of FIG. 1 must operate in such a way that the jet of the effluent from the feed nozzle 8 travels straightly and correctly into the receiver nozzle 9. If the jet does not move straight, it will collide with the inner wall of either the connecting passage 14 or the chamber 6 or the end of the receiver nozzle 9, resulting in the thermal decomposition of the sample or local cooling of the bombarded part. In the latter case, ice or front columns grow and clog up the connecting passage, deteriorating the rate of passage of the sample. However, since the diameter of the hole of the feed nozzle 8 is quite small, a slight change in the conditions in that portion necessarily disturbs the direction of the jet. Hence, the occurrence of the aforementioned undesired phenomena has been unavoidable. Another prior art system of combined liquid chromatograph/mass spectrometer is described in U.S. Pat. No. 4,298,795.